The present invention relates to an improved communication bus for use in integrated circuits based on low voltage swing logic.
Low voltage swing (xe2x80x9cLVSxe2x80x9d) circuits are known per se. Systems built upon such circuits typically carry data on a pair of wires. A first wire carries a true value of the data signal (D) and a second wire carries a complementary value of the data signal (D#). During a precharge phase, both the wires are precharged to a predetermined potential. During an evaluation phase, the potentials on the two wires diverge in response to the information content of the data signal. The LVS circuit generates an output response to voltage differences between the true and complementary signals.
LVS circuits are advantageous because they achieve higher data throughput than conventional xe2x80x9cfull swingxe2x80x9d logic circuit. In a xe2x80x9cfull swingxe2x80x9d circuit, a data signal typically transitions completely to either ground or Vcc before the circuit can generate an output signal. Because an LVS circuit can sense data from small voltage differences, LVS circuits realize faster operation and improved throughput than conventional full swing logic circuits. Further, because full swing transitions are not necessary to detect useful data, the voltages used within an LVS integrated circuit are reduced over a corresponding full swing circuit, thereby contributing to reduced power consumption.
Because each data signal is carried through the LVS circuit on a pair of wires, LVS circuits include twice as many metal tracks or wires between circuit elements than are in a corresponding full swing circuit. Although the metal pitch may be made tighter in an LVS circuit because of the reduced voltages, the doubling of wires in an LVS integrated circuit can lead to wiring congestion in the circuit. Such disadvantages can limit the applications for which circuit designers may choose to use LVS circuits.
Accordingly, there is a need in the art for an integrated circuit that possesses the speed and throughput advantages of LVS circuits but that also do not suffer the corresponding disadvantages of wiring congestion.
Embodiments of the present invention provide a communication bus for low voltage swing data signals that includes a wire for each of the low voltage swing logic data signals and a pair of wires for two reference signals.